Po Lu <luangruo@yahoo.com> writes:

> Paul Eggert <eggert@cs.ucla.edu> writes:
>
>>
>> Sorry, this is an area I know little about. (But I'll pontificate
>> anyway. :-)
>>
>> Perhaps the idea was that if you wanted modules written in C++, you
>> could compile Emacs with -fexceptions, even though this is not the
>> default build procedure. If so, I wouldn't worry too much about that,
>> as I don't think anybody does that.
>
> I'm not sure of the point of this since Emacs cannot survive a C++
> exception anyway.  Perhaps someone else will enlighten us.

-fexceptions is useful if it is possible to get a call stack which
invokes C++ through a C function through a C++ function, for instance,
if the comparator of a qsort could throw.  This provides the user of a
given C API to gracefully handle thrown errors.  Alternatively, it also
allows the C API developers to (mostly) gracefully clean up when a C++
exception remains uncaught.  This is why libc is compiled with
-fexceptions for instance.

__attribute__((cleanup)) will run cleanups during stack unwinding:

‘cleanup (CLEANUP_FUNCTION)’
     The ‘cleanup’ attribute runs a function when the variable goes out
     of scope.  This attribute can only be applied to auto function
     scope variables; it may not be applied to parameters or variables
     with static storage duration.  The function must take one
     parameter, a pointer to a type compatible with the variable.  The
     return value of the function (if any) is ignored.

     If ‘-fexceptions’ is enabled, then CLEANUP_FUNCTION is run during
     the stack unwinding that happens during the processing of the
     exception.  Note that the ‘cleanup’ attribute does not allow the
     exception to be caught, only to perform an action.  It is undefined
     what happens if CLEANUP_FUNCTION does not return normally.

IMO, the price of exceptions is overblown, so it could be worthwhile
adopting this, if I understand the context right.
-- 
Arsen Arsenović